1 files changed, 56 insertions, 1 deletions

diff --git a/crates/ra_hir_expand/src/lib.rs b/crates/ra_hir_expand/src/lib.rs
index dd07a16b4..b219b8fbf 100644
--- a/crates/ra_hir_expand/src/lib.rs
+++ b/crates/ra_hir_expand/src/lib.rs
@@ -12,11 +12,12 @@ pub mod hygiene;
 pub mod diagnostics;
 
 use std::hash::{Hash, Hasher};
+use std::sync::Arc;
 
 use ra_db::{salsa, CrateId, FileId};
 use ra_syntax::{
     ast::{self, AstNode},
-    SyntaxNode,
+    SyntaxNode, TextRange, TextUnit,
 };
 
 use crate::ast_id_map::FileAstId;
@@ -66,6 +67,30 @@ impl HirFileId {
             }
         }
     }
+
+    /// Return expansion information if it is a macro-expansion file
+    pub fn expansion_info(self, db: &dyn db::AstDatabase) -> Option<ExpansionInfo> {
+        match self.0 {
+            HirFileIdRepr::FileId(_) => None,
+            HirFileIdRepr::MacroFile(macro_file) => {
+                let loc: MacroCallLoc = db.lookup_intern_macro(macro_file.macro_call_id);
+
+                let arg_start = loc.ast_id.to_node(db).token_tree()?.syntax().text_range().start();
+                let def_start =
+                    loc.def.ast_id.to_node(db).token_tree()?.syntax().text_range().start();
+
+                let macro_def = db.macro_def(loc.def)?;
+                let shift = macro_def.0.shift();
+                let exp_map = db.parse_macro(macro_file)?.1;
+                let macro_arg = db.macro_arg(macro_file.macro_call_id)?;
+
+                let arg_start = (loc.ast_id.file_id, arg_start);
+                let def_start = (loc.def.ast_id.file_id, def_start);
+
+                Some(ExpansionInfo { arg_start, def_start, macro_arg, macro_def, exp_map, shift })
+            }
+        }
+    }
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
@@ -112,6 +137,36 @@ impl MacroCallId {
     }
 }
 
+#[derive(Debug, Clone, PartialEq, Eq)]
+/// ExpansionInfo mainly describes how to map text range between src and expanded macro
+pub struct ExpansionInfo {
+    pub(crate) arg_start: (HirFileId, TextUnit),
+    pub(crate) def_start: (HirFileId, TextUnit),
+    pub(crate) shift: u32,
+
+    pub(crate) macro_def: Arc<(mbe::MacroRules, mbe::TokenMap)>,
+    pub(crate) macro_arg: Arc<(tt::Subtree, mbe::TokenMap)>,
+    pub(crate) exp_map: Arc<mbe::RevTokenMap>,
+}
+
+impl ExpansionInfo {
+    pub fn find_range(&self, from: TextRange) -> Option<(HirFileId, TextRange)> {
+        fn look_in_rev_map(exp_map: &mbe::RevTokenMap, from: TextRange) -> Option<tt::TokenId> {
+            exp_map.ranges.iter().find(|&it| it.0.is_subrange(&from)).map(|it| it.1)
+        }
+
+        let token_id = look_in_rev_map(&self.exp_map, from)?;
+        let (token_map, file_offset, token_id) = if token_id.0 >= self.shift {
+            (&self.macro_arg.1, self.arg_start, tt::TokenId(token_id.0 - self.shift).into())
+        } else {
+            (&self.macro_def.1, self.def_start, token_id)
+        };
+
+        let range = token_map.relative_range_of(token_id)?;
+        Some((file_offset.0, TextRange::offset_len(range.start() + file_offset.1, range.len())))
+    }
+}
+
 /// `AstId` points to an AST node in any file.
 ///
 /// It is stable across reparses, and can be used as salsa key/value.